Light intensity dependence of organic solar cell operation and dominance switching between Shockley-Read-Hall and...

We investigated the variation of current density-voltage (J-V) characteristics of an organic solar cell (OSC) in the dark and at 9 different light intensities ranging from 0.01 to 1 sun of the AM1.5G spectrum. All three conventional parameters, short-circuit currents (J_sc), open-circuit voltage (V_oc), and Fill factor (FF), representing OSC performance evolved systematically in response to light intensity increase. Unlike J_sc that showed quasi-linear monotonic increase, V_oc and FF showed distinctive non-monotonic variations. To elucidate the origin of such variations, we performed extensive simulation studies including Shockley-Read-Hall (SRH) recombination losses. Simulation results were sensitive to defect densities, and simultaneous agreement to 10 measured J-V curves was possible only with the defect density of [Formula: see text]. Based on analyses of simulation results, we were able to separate current losses into SRH- and bimolecular-recombination components and, moreover, identify that the competition between SRH- and bimolecular-loss currents were responsible for the aforementioned variations in J_sc, V_oc, and FF. In particular, we verified that apparent demarcation in V_oc, and FF variations, which seemed to appear at different light intensities, originated from the same mechanism of dominance switching between recombination losses.